Software

Ask something
Question Locked

Cell phone interference

0 helpful
8 replies

by rfci99 1 view

Closed to new repliesThis discussion is closed. It stays readable, but it takes no new replies.

The situation I have is that, If the computers on the main Floor are turned on, Cell phones in the lower level will not work!

Cell phones in the computer room work just fine either way.

The network cabling (CAT-5) has been tested and no faults were found.

The phone wiring to the computer room has been tested and no faults were found.

When the computers are turned off There are no problems whatsoever.

Any suggestions?

Please email me directly on this issue.

Thanks

8 replies

by thechas

First off, what is the building construction?

And, how clean is the AC power?

My suspicion is that you have marginal signal on the cell phones to begin with, and only a little interference will knock out reception.

Most commercial buildings have lots of metal in them that is connected to ground. This forms a fairly decent shield cage. Not only does this shield reduce reception, it also traps the noise from the computers and to some amount, makes any RF noise source have a greater effect than it normally would.

Anyhow, I suspect you will find that noise on the AC power lines will have a greater impact than anything on the CAT 5 cable.

You can try working with the most common cell phone service provider and see what they can suggest to improve reception.

You could also hire a good old HAM radio operator as a consultant to help find and reduce sources of the interference.

Chas

by rfci99

Building type is bi-level residents

I will check the power, however when none of the computers are powered up, The signal is fine. Also other cell phones work no matter what.

by thechas

This statement has me confused:

"other cell phones work no matter what"

Does this mean that the problem is with phones from a specific carrier?

If so, checking the signal strength on a phone with the problem both with and without the computers on would be a very valuable data point.

In our office building, where people get a usable signal depends on who their carrier is. Some need to go to the South, others to the North. In the center of the building, it makes little difference who your carrier is, very few people get any signal.

Then again, with all of the electronic equipment we have, the transmitter needs to almost be line of site to expect a signal.

Chas

by rfci99

The cell phones all work upstairs, even in the computer room.

The lower level has good signal strength when the computers are off. When the computers are on we have problems on the lower level.

by thechas

I would have your electrician check the ground resistance on multiple outlets on the lower level.

If ground checks out fine, then you need to know what is happening. The best way to do this is to sweep the office with a spectrum analyzer with the computers on and off.

Once you identify the frequency that is the problem, you may be able to underclock some of the computers to reduce the amount of RF noise at the critical frequency.

If the spectrum analyzer is sensitive enough, you might even be able to track the source down to 1 or 2 systems that may have bad grounds or other problems.

A large HAM radio club might have the right equipment and be willing to help out for a nominal charge.

Chas

by rfci99

Chas,
Thank you very much for your help on this. I am going to contact a friend who is a ham. I think that your line of thinking is correct.

Please feel free to contact me in the future if I can be of help in any help in anyway. Thanks again.

Richard Fulsom

Direct 720-296-3231

rfulsom@rfinvestigations.com

by thechas

For your own benefit, I recommend that you edit your last post and remove your contact details.

This is a very public forum and it is not a good idea to publish phone numbers and full email addresses.

There are nefarious people who troll these forums and harvest contact information.

A better way to share contact information here at TR is to make use of the Peer Mail function. I may not respond to every peer mail that I get. But, I do read them and save many of them.

If you do not have success with the ground integrity of spectrum analyzer, one very good resource is DLS Labs in Wheeling Illinois. They have been dealing with RFI since nearly the dawn of electronics. While they are more focused on product compliance testing, they still make field calls and site checks.

Chas

This discussion is closed to new replies.